Transmission line termination



5. H. WALKER TRANSMISSION LINE TERMINATION Filed NOV. 16, 1962 June 1, 1965 NW mm W w /////n/ w INVENTOR. scorr H. WALKER my a ATTORNEY United 1 States Patent 3,187,276 TRANSMISSIGN LINE TERMLNATION Scott H. Walker, Gaithershurg, Md., assignor to The Bendix Corporation, Son-thfield, Mich., a corporation of Delaware Filed Nov. 16, 1962, Ser. No. 238,196

3 Claims. (Cl. 333-22) This invention relates to an improved termination for a coaxial transmission line.

The characteristic impedance of a' coaxial transmission line is purely resistive. Accordingly, if the line is terminated in a resistance of proper value there should be no reflections. However, it is difficult to obtain a purely resistive termination because the terminating resistors which are used contain inductive reactances due to their geometry and finite size.

In accordance with this invention, a conductive slug is disposed between inner and outer conductors in electrical contact therewith. A terminating resistor inserted in the inner conductor has one end in electrical contact with the slug through the inner conductor. The capacitive reactance provided between the slug and the other end ofthe resistor as a result of predetermined spacing between them compensates for the inductive reactance introduced by the resistor and a very pure resistive termination is obtained.

Accordingly, it is an object of this invention to provide "ice j is inserted adjacent to the insulator 34 between the section 28 of the conductor 26 and the member 18. The insulator 36 is made a particular length so that the end face 38 thereof is at a desired distance from the end 40 of the resistor 30.

An annular conductive slug 42 made of a conductive material such as brass is inserted adjacent to the insulator 36 in electrical contact with the retainer 32. Since the slug 42 is adjacent to the insulator 36, its inner face 44 is also at the desired distance from the end 40 of the resistor 30. The slug 42 is fixed within the member 18 by solder 46. a

The resistor 30 is selected to have a value of resistance substantially equal to the characteristic impedance of the coaxial transmission line it is desired to terminate. The coaxial line connector (not shown) is-screwed into the threaded portion 16 so that the center conductor of the coaxial line makes electrical contact with the center conductor 26. IA gasket 48 made of a suitable insulating material is provided on the member 18 so as to seat the coaxial line connector.

an improved termination for a coaxial transmission line wherein capacitive reactance is provided to compensate for inductive reactance introduced by a terminating resistor.

It isanother object of this invention to provide an improved termination of the above character which operates efiectively over a broad frequency range.

It is a further object of this invention to provide an improved termination of the above character which is reliable in its operation and is extremely simple to manufacture on a mass production basis.

Other objects and advantages will become apparent from the following detailed description and from the appended drawing and claims.

In the drawing, the single figure is a cross sectional view of an embodiment of this invention;

The terminating device of the present invention generally indicated at 10in the drawing is connected to a conventional coaxial connector generally indicated at 12.

The connector 12 includes a tubular member 14 made of a conductive material such as brass with threads 16 on the inner surface thereof. The terminating device 10 includes a tubular member 18 made of a conductive material such as brass which is inserted into the member 14. An annular snap ring 20 positioned in annular grooves 22 and 24 of members 18 and 14 respectively, secures the member 18 within the member 14.

Disposed axially within the member 18 is a center conductor 26 made of a material such as brass. One end of the conductor 26 has a section 28 of larger diameter provided with a hole 29 to receive one end of a commercially available resistor 30 which is soldered tothe section 28. In one termination device that was constructed,

a 50 ohm resistor manufactured by the Film Resistor Corporation was used. This resistor having a diameter of In accordance with the present invention, the undesirable inductive reactance introduced by the terminating resistor 30 is compensated for by the capacitive reactance provided between the end face 44 of the slug 42 and the end 49 of the resistor 30. As previously indicated, the face 44 is positioned at a particular distance from the end 40 to provide the desired amount of capacitive reactance to compensate for the inductive capacitance.

An important advantage of the termination device of the present invention is that it is relatively simple to manufacture on a mass production basis. For coaxial lines having a particular characteristic impedance, once it is determined what distance should be maintained between the end face 44 of the slug 42 and the end 40 of the resistor 35 to provide the necessary compensation, then this determines the length of the insulator 36 that must be used to provide the proper spacing. With an insulator 36 of proper length, it becomes a simple matter during assembly of the termination device to insert the insulator and then to insert the slug 42 adjacent thereto to achieve the necessary compensation.

Another important advantage of the termination device described herein is that it operates effectively over a very broad frequency range. For example, in a 50 ohm termination device that was built, the voltage standing wave ratio did not exceed 1.1 over a coaxial frequency range of D.-C. to 12.6 gigacycles.

Although this invention has been disclosed and illustrated with reference to particular applications, the principles involved are susceptible of numerous other applications which will be apparent to persons skilled in the art. The invention is, therefore, to be limited only as indicated by the scope of the appended claims. Having thus described my invention, I claim: 1. device for terminating the end of a coaxial line comprising a conductive outer member of tubular configuration, a conductive inner member disposed axially within the outer member, s

a resistance axially disposed within the outer member and having its first terminal in electrical contact with the inner member,

an insulating annular member disposed between the inner and outer members and extending to a position between the first and second terminals of the resistance,

and a conductive annular slug disposed within the outer member in contiguous relationship with the annular member to provide capacitive reactance between the slug and the first terminal of the resistance, said slug also providing electrical communication between the A assists i atented June 1, 1965 second terminal of the resistance and the outer a conductive inner member disposed axially Within the member. outer member, 2-

f ev f! tel'mlflatlng the end of a COaXlal 11m a resistance disposed axially within the outer member COmPIISmg, 1 7 and having its first terminal in electrical contact with a conductive outer member of tubular shape, the inner member, first and sewed conducme F ,m g of g a conductive annular member disposed within the outer ShaPe disposed anally wlthlr} 6 Outer. mem member in electrical-contact therewith and having its a cylmdncany Shaped reslstance dlsposed axlany with inside surface positioned relative to the first termiin the outer member between the first and second inner members and having its first and second termi- 1O nals in electrical contact with the first and second inner members respectively, an insulating annular member disposed between the outer member and first inner member and extending to a position between the first andsecond terminals of theresistance, a N v and a conductiveannular slug disposed between the References Cue?! by the Examiner v outgr member and the $203M inntler membter and ex 3 UNITED STATES PATENTS ten ing into contact wi t e annu ar mem erto. r0- y v vide a desired capacitive reactanc'ebet ween the s lug 2704348 3/55 Carhn nal to provide a desired-amount of capacitive'reactance between said surface and saidterminal for compensation of the inductive reactance introduced by a the resistance, l and means for electrically connecting; the annular memher. to the second'term'ina'l of the resistanc'ei and the first'terminal of the resistance, said slug also f 4/59 SteYens ifgi v providingan electrical short between the second inner 0 15 '6 j Wefnschal r member'and the outer'membcr; 7 3,005,967 lO/6l Wemschal 333-81 3. A device for terminating the end'of a coaxial line comprising V HERMAN- KARLYSA'ALBACH, Primary Examiner. a conductive outer member of tubular shape, V V t 

1. A DEVICE FOR TERMINATING THE END OF A COAXIAL LINE COMPRISING A CONDUCTIVE OUTER MEMBER OF TUBULAR CONFIGURATION, A CONDUCTIVE INNER MEMBER DISPOSED AXIALLY WITHIN THE OUTER MEMBER, A RESISTANCE AXIALLY DISPOSED WITHIN THE OUTER MEMBER AND HAVING ITS FIRST TERMINAL IN ELECTRICAL CONTACT WITH THE INNER MEMBER, AN INSULATING ANNULAR MEMBER DISPOSED BETWEEN THE INNER AND OUTER MEMBERS AND EXTENDING TO A POSITION BETWEEN THE FIRST AND SECOND TERMINALS OF THE RESISTANCE, AND A CONDUCTIVE ANNULAR SLUG DISPOSED WITHIN THE OUTER MEMBER IN CONTIGUOUS RELATIONSHIP WITH THE ANNULAR MEMBER TO PROVIDE CAPACITIVE REACTANCE BETWEEN THE SLUG AND THE FIRST TERMINAL OF THE RESISTANCE, SAID SLUG ALSO PROVIDING ELECTRICAL COMMUNICATION BETWEEN THE SECOND TERMINAL OF THE RESISTANCE AND THE OUTER MEMBER. 